The present invention relates generally to access panels and more specifically to an access panel in motor control centers to inspect bus bar connections.
Motor control centers are commonly employed for performing various protection and control functions in industrial settings. In such motor control centers, three-phase electric power is fed from electric power distribution mains to the motor control center through a main circuit breaker within the control center. Within the motor control center housing, internal electric power is fed from the main circuit breaker to control center electrical components through horizontal and vertical main bus conductors. Electrical power is then fed through the bus conductors to internal electrical components mounted within the drawers or buckets. The buckets contain devices such as one or more circuit breakers, starters, overload protectors, or pilot devices. Electrical connection between the main vertical bus conductors and between the main circuit breaker and the main vertical bus conductors and the distribution bus conductors require suitable attachment hardware such as bolts. Further, high contact pressure is necessary to obtain a good electrical connection.
Bus conductors usually extend within a control center enclosure where the respective electrical connections are made. The associated buses are arranged within the control center enclosure and accessed by means of a cabinet or panel positioned on the front wall of the enclosure. Such enclosures have fixed back, side and top walls.
Where bolts are used to maintain bus to bus connections, the torque of the bolts must be checked periodically to assure the integrity of the connection. A loss of torque in the connection can lead to unwanted heat rise. Excess heat may also cause condensation and corrosion. It is also desirable to visually inspect energized connections while maintaining a safety barrier between connection and personnel. Further, it is desirable to measure the temperature of individual energized connections during operation without exposure of personnel to a high voltage connection.
Access panels of the prior art have provided access to bus connections by the use of sliding or pivoting panels that open to expose more than one phase of the current. Therefore, personnel cannot isolate one connection at a time but rather must expose more than one phase. In the prior art, an insulating barrier is not maintained during non-contacting temperature measurement nor is such barrier maintained during visual inspection. In order to visually inspect the high voltage connections, the panel must be opened which does not provide any insulating barrier between the connection and the personnel.
In an exemplary embodiment of the invention, an access panel made of an electrically insulating material comprises a surface having a plurality of apertures disposed therein, with the apertures positioned to align with one or more bus bar connections. A plurality of covers is pivotally mounted on the surface of the panel from a point adjacent to the apertures, each aperture having one corresponding cover. The covers are configured to be moveable between an open and closed position. In the open position, the covers are pivotally rotated to provide access to the aperture. The positional relationship of the apertures and respective covers along the surface of the panel determines the access to at least one bus connection.